Jet engine fuel control



Sept. 1, 1953 K. J. KNUDSEN 2,650,471

JET ENGINE FUEL CONTROL Filed July 5, 1947 2 Sheets-Sheet 1 F u v 9INVENTOR. Knudsew llllllllllllll't [0s m: @N.

ATTORNEYS P 1, 1953 K. J. KNUDSEN 2,650,471

JET ENGINE FUEL CONTROL Filed July 5, 1947 2 Sheets-Sheet 2 F"" I l I II l l L.

EB N

ATTORNEYS Patented Sept. 1, 1953 JET ENGINE FUEL CONTROL Knud J.Knudsen, Woodbury, Conn., assignor to The Lewis Engineering Company,Naugatuck, Conn., a corporation of Connecticut Application July 5, 1947,Serial No. 759,262

50 Claims. 1

This invention relates to the throttling or control of fuel injet-turbine aircraft engines, for controlling engine speed or power, andtemperature.

An object of the invention is to provide an improved method of controland an improved manually-settable, automatic regulating fuel controldevice for a jet-turbine engine whereby an extremely quick-actingregulation is had in response to changes in the setting of the device,with the result that dangerous overheating and racing of the engine isprevented.

Another object of the invention is to provide an improved regulatinjet-engine fuel control method and device whereby for any throttlesetting the engine temperature and speed or power will be accurately andreliably maintained within a relatively narrow range.

A further object of the invention is to provide improved indicatingmeans in conjunction with a regulating, settable fuel control for ajet-turbine engine as characterized above.

Still another object of the invention is to provide, in a jet-enginecontrol device as above, improved and quick-acting automaticallyoperative means for opening or closing the throttle in response toconditions caused by sudden climbing or diving of the aircraft, therebyto quickly limit the engine temperature and speed to a safe value duringsuch maneuvers.

Yet another object of the invention is to provide a regulatingjet-engine control as above, having reliable safety means for closingthe throttle when the engine temperature becomes dangerously high,thereby to prevent damage and inoperativeness of the engine.

Another object of the invention is to provide a control device havingcharacteristics as above, which is of relatively simple and economicalconstruction and is reliable in operation over an extended period ofuse.

A further object of the invention is to provide a regulating controlaccording to the foregoing and wherein a changeover may be quickly andeasily eifected from automatic to manual control and vice versa.

In accomplishing these objects there is provided, according to theinvention, a novel method and apparatus whereby a. deflectable member ismade to continually and rapidly move back and forth or oscillate with anamplitude and period which is proportionate with the temperature of theengine, this being effected in part by a heatresponsive means. Thisoscillating movement, through a novel relay device which in oneembodiment of the invention comprises a bank of blocking, relay vacuumtubes, is made to actuate a reversibly movable powered means in such amanner that the said means moves in one direction when the amplitude andperiod of oscillation of the member are greater than a predeterminedvalue, and moves in the other direction when the amplitude and periodare less than said value.

The powered means is connected to drive the fuel valve of the engine,thus to effect an automatic control.

The defiectable member of the control is made to rapidly oscillate by anorganization which I term an anticipator and which includes a componentactuated concurrently with movement of the powered means and fuel valve,said component being connected to influence a driving means for thedefiectable member, which driving means is connected to theheat-responsive means under the control of the temperature of theengine. The term anticipator is applied to this organization since itanticipates the effect, on the heat-responsive means, of a change inengine temperature, as will be later brought out in detail.

The above assemblage, except for the fuel valve, constitutes in generalan oscillatory actuator device, since it is arranged to be,independently of the engine temperature, in a state of continualoscillation or hunting, and by virtue of this an extremely rapidregulation is had in response to engine temperature changes, or tointended changes in the setting of the control, this being accomplishedin spite of a relatively great time lag being present in thetransmission of heat from the engine to the heatresponsive means of thecontrol. By this organization I effectively prevent overheating andracing of the engine, which may be of great danger in jet-turbineengines, resulting in inoperativeness and destruction.

In the specific embodiments of the invention illustrated herein thedeflectable member and driving means therefor are parts of a sensitiveinstrument movement, and include the movable coil and field of saidmovement, which coil is connected with the heat-responsive means to becontrolled thereby. The said movable coil controls contacts within theinstrument movement which trigger the relay vacuum tubes, the latter inturn actuating the powered means which operates the fuel valve of theengine. Throttling is accomplished by a settable throttle member whichvaries a resistor included in the circuit a from the heat-responsivemeans to the instrument coil, said variation changing the relationshipof the amplitude and period of oscillation of the deflectable member orcoil of the instrument movement with respect to the temperature of theengine. Due to the sensitivity and accuracy of the components of theinstrument movement, together with the oscillating or continuallyhunting characteristics of the control, the temperature of thejet-engine is held to narrow limits for a given throttle setting, and bythe provision of suitably marked graduations at the throttle, thetemperature of the engine may be indicated within close limits.

By cutting in or out, in its entirety, the throttling resistor thetemperature and consequently speed of the engine may be readily fullyincreased or decreased, and this resistor is therefore utilized inconjunction with relays and a propeller-acceleration responsive deviceto automatically quickly control or regulate the engine if the aircraftshould unexpectedly climb steeply or dive, thereby to safeguard againstexcessive engine temperatures.

A second sensitive-instrument movement is provided, parallel connectedwith the first movement as regards the heat-responsive means, and havingmovable-coil controlled contacts so arranged and connected that, shouldthe engine temperature become too great, the control will be taken awayfrom the settable throttle of the device and the fuel valve will beautomatically closed to reduce the fuel flow and consequently thetemperature. Upon temperature reduction occurring, the settable throttleis automatically 1 restored to control, and this organization thereforeprovides further for safety in the operation of the engine. The secondinstrument movement also provides a safety factor in that it will assumecontrol to reduce the fuel supply if the first sensitive instrumentmovement should fail in its functioning.

The relay vacuum tubes and powered means controlled thereby are soarranged, as regards their energization, that changeover from automaticto manual control and vice versa is easily and quickly accomplished byuse of a relatively simple circuit and switching means. To prevent delayin the changeover, the energization of the vacuum tubes is continuedduring manual operation, thereby enabling the control to be immediatelyeffective when switched to automatic operation, without requiring awaiting period.

The entire control device, comprising the contact-controlling instrumentmovements, the

vacuum tube relay means, reversible powered means for the fuel valve,and the anticipator mechanism, is of simple construction and involvesrelatively few parts considering its purpose and function, and istherefore relatively economical to manufacture.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure 1 is a schematic diagram showing one form of the control devicemade according to the invention, the device being illustrated inconnection with a jet-turbine engine and fuel valve controlling thelatter, and

Figure 2 is a schematic diagram showing another form of the controldevice made according to the invention, applied to a jet-turbine engineand fuel valve control therefor.

Referring to Fig. 1, a jet-turbine aircraft engine It is shown, the saidengineilieing powered by a heating medium such as a liquid fuel, and.the engine having a casing I l and turbine rotors l2 and I3 carried by ashaft [4, on which latter the aircraft propeller I5 is mounted.

The propeller [5 may be of the fixed pitch type, in which eventincreasing the fuel supply to the engine It) will result in an increasein the speed of the shaft [4; or the propeller may be of the variablepitch type, in which case increasing the fuel supply and simultaneouslychanging pitch may result in a power increase with substantiallyconstant shaft speed.

The temperature and speed or power of the engine IE9, constitutingvariables, are controlled by a reversible control device It comprising aflow-control means in the form of a fuel valve which governs the flow offuel to the casing II, and within the latter a heat-responsivetranslating device H is mounted, the said device being preferably athermocouple having terminals I 8 and IS. The thermocouple H may belocated in any desirable place in the casing I I, being shown, however,as located ahead of the turbine rotor I3. The response of thethermocouple ll to a change in the temperature of the engine In mayinvolve generally a time lag of approximately fifteen seconds.

The present invention provides an improved settable control inconjunction with the thermocouple l for automatically maintaining thetemperature and speed or power of the jet-turbine engine It] within anyselected one of a plurality of different predetermined ranges, as forexample, ranges within a low limit of 900 F. corresponding to idlingspeed of the engine, and a high limit of 2200 F. corresponding to arunning speed at full power, of the engine, without danger ofoverheating of the engine due to a change of setting, or due to othercircumstances.

This control is indicated as comprising two separate units, a fuel-valveactuator unit 20 blocked off by a broken outline 20a, and a control unit2| blocked off by a broken outline 2 la; however it should be understoodthat the various components of the control and circuits therefor may besegregated differently from the arrangement shown.

The units 20 and 2| together constitute an oscillatory actuator devicein that they include a powered means for actuating the fuel valve l6,and in that the device is in a continual state of oscillation or huntingwhich is sustained independently of connection to the thermocouple H.The arrangement is such, however, that the thermocouple i! may controlthe period of oscillation and amplitude of the oscillating parts, withinlimits, thereby to ultimately control the setting of the fuel valve l6,and the method of control and organization of parts is such that thecited time lag of fifteen seconds between the thermocouple i6 andtemperature of the engine [0 is anticipated, so to speak, in a manner toprevent wide swings of temperature of the engine beyond the settings ofthe control, and to provide an overall response time or time ofregulation on the order of two seconds, the said time interval occurringbetween a change in the setting of the control and the establishment ofthe new temperature range in the engine Ill.

The fuel-valve actuator unit 20 comprises a reversible powered means 22which may be a Lear model -A or model 1l9-D actuator, such actuatorconsisting of an electric motor energized through terminals 23 and 24and driving a shaft 2 5 the rotation and direction of turning of whichis controlled by electrically operated clutches energized throughterminals 26, 27 and 28, 29 respectively. The shaft 25 of the poweredmeans 22 carries a capstan 30 which is mechanically connected to drivethe fuel valve I6 in one direction or the other, as indicated by thebroken line 3i.

The actuator unit also includes part of the anticipator mechanism of thecontrol, comprising an arm 32 mounted on the shaft by means of a splitcollar 33, said collar having a pair of ears 34 continually urgedtogether by a screw 35 and compression spring 36 carried by the screw.The arm 32 is thus frictionally mounted on the shaft 25 and may remainstationary while the shaft rotates in either direction.

Movement of the arm 32 between limits is made to control an electricalcircuit, and for this purpose the arm has a projection 31 engageablewith a pivotal contact arm 38 which is in turn cooperable with astationary contact 39. Stops 40 and 4| are respectively engageable withthe arms 38 and 32 to limit movement of these, and an extension spring42 connects the arm with the stop 4I. By this organization clockwiserotation 01' the shaft 25 causes engagement between the contact arm 38and contact 30, and counterclockwise rotation of the shaft 25 causesdisengagement between the contact arm 30 and contact 30. As will belater described, the arm 38 and contact 39 are connected with thecontrol unit 20 for the purpose of setting up a continuous rapidoscillation of the control device.

The control unit 2I comprises an electro-receptive instrument 43 in theform of a sensitiveinstrument relay which may be of the type disclosedin my copending patent application S. N. 612,272, filed August 23, 1945,now Patent No. 2,508,862, and entitled Electrical Relay. The instrumentor relay 43 includes a permanentmagnet D. C. instrument movement, andhas a movable coil 44 carrying a contact arm 45 which latter iscooperable with a stationary contact 46. The arm 45 constitutes adeflectable member which is movable between advanced and retractedpositions. The coil 44 of the movement, when energized is deflectedtogether with the arm 45, and said coil is connected by a wire 41through a connector fitting 48 and wire 49 to the terminal I8 of thethermocouple IT. The coil 44 is also connected by a wire 50 to one endof a resistor 5I hereinafter also termed a throttle resistor, the otherend of said resistor being connected by a wire 52 to one end of a secondresistor 53, which I also term an anticipator resistor.

The remaining end of the anticipator resistor 53 is connected by a wire54 through the connector fitting 48 and a wire 55 to the other terminal19 of the thermocouple H. The instrument coil 44 is thus energizedthrough the resistors 5! and 53 from the thermocouple I1.

The contact arm 45 and stationary contact 46 are connected to a novelrelay means 56, inclucling a pair of vacuum tubes so arranged thatoperation of one tube blocks operation of the other tube and vice versa,all for the purpose of energizing one or the other of the clutches ofthe powered means 22 respectively according to whether the contacts 45,45 are engaging or not engaging each other. A safety device is alsoincorporated in the control circuit for the said relay means and isoperative to cause actuation of the powered means 22 and closing of thefuel 6. valve is if the temperature. of the engine [0 should exceed apredetermined extreme value.

The safety device comprises a second electroreceptive instrument in theform of a sensitiveinstrument relay 51 which may be similar to the relay43, having a movable coil 50 and a contact arm 5-9 driven by the coiland engageable with a cooperable stationary contact 60. The movable coil58 of the relay 5! is connected by wires BI and 62 through the connectorfitting 48 respectively to wires 63 and 64, which are in turn connectedrespectively to the terminals I9 and I8 of the thermocouple II. Thus,the coil 58 is energized from the thermocouple II simultaneously withenergization of the coil 44.

The blocking relay mean 56 controlled by the contacts 45, 46 of theinstrument relay 43 includes vacuum tubes 65 and- 05, which may be type6AK5, the control grid 61 of the tube 66 being connected by a wire 67ato one end of a grid resistor 60 (which may be of two megohmsresistance), the other end of which resistor is connected by a wire 60with the stationary contact 46 of the instrument relay 43. Both heatersI0 of the vacuum tubes 65 and 66 are connected in parallel by wires IIand I2, the latter wire being connected with the contact arm 59 of thesafety relay 51, and the stationary contact 60 of the safety relay beingconnected by a wire 13 with the contact arm 45 of the instrument relay43. The contact means of both of the instrument relays 43 and 51 arethus connected in series so as to control the polarization oi thecontrol grid 51 of the vacuum tube 60, and in connection with suchpolarization, a wire I4 connects the wire I2 of the vacuum tube heaterswith a jumper wire '55 connected between the oathodes I6 and 17 of thetubes 65 and 66 respectively.

The heaters 10 of the vacuum tubes are energized from a filament windingI8 (which may be 6 volts) of a power transformer I9 having a primarywinding connected with supply terminals 8I, the said filament windinghaving one end connected by a wire 82 to the wire 12 and having itsother end connected to the wire II.

The wire 69-is also connected to one end of a grid leak or bleederresistor 83 (which may be of 20 meghoms resistance), the other end ofwhich resistor is joined by a wire 84 to a ground connection 85. Thewire 12 is connected by a wire 86 to a resistor 8! (which may be of 600ohms resistance), the said resistor being connected to a wire 88 joinedwith the control grid 80 of the vacuum tube 55, and being connected to asecond resistor 90 (which may also be of 600 ohms resistance), thelatter resistor being joined to a ground connection 9|. Positivepotential for the anodes 92 and 93 of the vacuum tubes 65 and 60 issupplied from a high voltage winding 94 of the power transformer I9, andthe said winding may have a voltage of H5. The winding 94 has one endconnected by a wire 05 to a ground connection 95 and has its other endconnected by a wire 0'! to a rectifier 98, which is in turn connected bya wire 99 to one end of which a pair of drop resistors I00 and IOI(which may be of 10,000 ohms resistance each), the other ends of saidresistors being connected by wires I02 and I03 with screen grids I04 andI05 respectively of the vacuum tubes 65 and 66. A condenser I06 isconnected between the wires 95 and 9'! to smooth out the rectifiedoutput of the transformer winding 94.

The wires I02 and I03 in the anode circuits of the vacuum tubes areconnected by wires III! and I08 through a connector fitting I99 to wiresIII! and III respectively. The wires III] and III connect to limitswitches II2 and II3 respectively, the other terminals of said switchesbein connected by wires H4 and II5 to the clutch energization terminals29 and of the powered means 22. The limit switches II2 and H3 arenormally closed as shown, and are arranged to be actuated by a cam IIBcarried on the shaft 25 of the powered means when the shaft reaches itsextremity of movement in one direction or the other. Actuation of eitherof the limit switches H2 and H3 opens the circuit of that one of theclutches of the powered means 22 which has been operative to drive theshaft 25 to its extremity of movement, and therefore, further turningforce is removed from the said shaft.

The anodes 92 and 93 of the vacuum tubes 65 and 66 are connected bywires Hi and M3 to a manually operable rotary selector switch H3, whichhas wires I29 and I2I leading from it and connected through theconnector fitting I99 with wires I22 and I23 which are respectivelyconnected with the clutch terminals ill and 23. When the selector switchI I9 is in operative position for automatic operation of the control,indicated by A in Fig. l, the wires II! and IIS thereof are respectivelyconnected with the wires I29 and I 2I.

The motor terminals 23 and 24 of the powered means 22 are connected bywires I at and I25 through the connector fitting I99 respectively to thewires I26 and I21, the wire I26 leading to a pair of supply terminalsI28 and the wire I 21 leading to the selector switch H9. A wire I29leads from the selector switch M9 to the other supply terminal of thepair I28. When the selector switch H9 is in position for automaticoperation, the wires I21 and I29 are connected together, therebyeifecting energization of the motor of the powered means 22 from thesupply terminals I28.

Referring back to the energizing of the instrument relay 43, thisenergization is controlled by a slider contact I39 on the throttleresistor 5I, the said contact being actuated by a throttle lever I3Iwhich is movable over a graduated scale I32. The slider contact I39 isconnected by a wire I33 with a contact I34 of a relay I35 having acooperable contact I35 connected by a wire I3I with the wire 52. Thecontacts l34 and I35 of the relay I35 are normally closed, and thepurpose of the relay itself will be disclosed later in detail.

Further control of the energization of the instrument relay 43 isexercised by the anticipator resistor 53, this resistor being in turncontrolled by the movements of the powered means 22 by virtue ofconnections as follows:

The wire 54 connected to the resistor 53 is also connected by a wire I39to the contact arm 38 actuated by the driving arm 32 on the shaft 25 ofthe powered means 22, and a wire I39 connects the wire 52 from theresistor 53 to the stationary contact 39 which is cooperable with thearm. 38.

According to the above organization, when the supply terminals BI andI29 are energized from suitable sources, the parts 29 and H of thecontrol device will be in a state of oscillation or hunting, and uponthe thermocouple I? being heated in response to operation of thejet-turbine engine ID, the fuel valve I6 will be automaticallycontrolled or regulated to maintain the engine temperature within apredetermined range. This is accomplished as follows: Considering therotary switch I I9 as set for automatic operation, wherein the wiresI29, I I I and I I8 are respectively connected to the wires I21, I20 andI2I, and assuming that the throttle lever I3I is set in a givenposition, and that the engine I0 is operating at a predetermined safetemperature, the thermocouple I! will be heated and will cause anenergization of the coil 44 of the instrument relay 43. If thisenergization is below a predetermined value, the movable contact 45 ofthe instrument relay 43 will engage the stationary contact 46 thereof,as shown in Fig. 1. Also, for safe operating temperatures of the engineIII the movable contact 59 of the instrument relay 51 will be engagingthe stationary contact 60 thereof as shown.

For the above conditions the contact arm 38 may initially be separatedfrom the stationary contact 39, thereby enabling the anticipatorresistor 53 to be operative in the energizing circuit for the coil 44 ofthe instrument relay 43. As a consequence of these positionings of theparts, the vacuum tube 63 will now be made operative, in the followingmanner: A circuit will be established between the cathodes T5 and II ofthe vacuum tubes 65 and 66, through the wire I2 and instrument relays 51and 43 to the wire 69, and will cause the latter to assume the potentialof the said cathode. Assuming that the ground potential is zero, andthat the potential of the wire 99 from the high voltage coil 94 of thepower transformer I9 is I I5, and assuming that the vacuum tube 65 isconducting (i. e. passing an electron stream between its cathode andanode) a voltage drop will exist across the combined resistors 81 and 99(due to the anode current passing therethrough) which may be in theneighborhood of '7 volts, and therefore, the polarity of the cathodes I6and II with respect to ground will be approximately 7 volts. Due to theconnection between the wire 69 and the cathodes as effected by theinstrument relays 5'! and 43, the polarity of the wire 69 with respectto ground will also be approximately '7 volts. As a consequence of theproportioning of the grid resistors 68 and 83, most of this '7 voltpotential of the wire 63 will be impressed on the control grid 61 of thevacuum tube 66, and this relatively high positive potential, almost thatof the cathode 11, together with the much higher potential on the anode93 of the tube 95 will cause the latter to be conducting. This conditiontherefore results in energization of the clutch, of the powered means22, which is connected with the terminals 28 and 29 and also causes arelatively high voltage drop across the resistor I09. Energization ofthe clutch connected with the terminals 28 and 23 causes clockwiserotation of the shaft 25, since the motor of the powered means 22 isbeing energized from the supply terminals I28. Immediately upon theshaft 25 starting its rotation the arm 32 carried thereby will be swungclockwise or to the left and will drive the contact arm 38 to the leftso as to engage the stationary contact 39. This will immediately excludethe anticipator resistor 53 from the energizing circuit for theinstrument relay 43, and will therefore cause immediate increase in thecurrent passing through the coil 44.

The voltage drop across the resistor IO!) will reduce considerably thepotential on the screen grid I93 of the vacuum tube 65, such reductionbeing sufficient to stop the tube from being con- 9 ducting, that is,sufficient to not sustain the flow of electrons to the anode 92 of thetube from the cathode 16.

Preferably the amount of current increase caused by exclusion of theanticipator resistor 53 is equivalent to the current increase whichwould be caused by the temperature of the thermocouple ll being raisedapproximately 400 F. The increase of current occasioned by exclusion ofthe anticipator resistor 53 results in the movable contact 45 of theinstrument relay 43 being quickly swung to the right and separating fromthe stationary contact 46 thereof. Upon this occurring the potentialimpressed on the wire 69 by its connection through the instrument relays43 and 51 with the cathodes l8 and H is removed, thereby immediatelycausing a reduction in the positive potential of the control grid 61.

The vacuum tube 66 now tends to become nonconducting since the positivepotential of the control grid 8! thereof is insufficient to sustain in astable condition the electron stream from the cathode H to the anode 93,and the said electron stream therefore becomes reduced. Reduction ofsaid electron stream largely wipes out the voltage drop across theresistor Hill and therefore the wire [02 is charged with a relativelyhigh positive potential which approaches in value that of the wire '99,the said potential being therefore applied to the screen grid I04 of thevacuum tube 65. This high potential on the screen grid H14, togetherwith a positive potential (measured from ground) on the control grid 89resulting from connection of the latter through the wire 88 to thecommon connection between the resistors 81 and 96 causes the vacuum tube'65 to again become conducting even though the grid 89 is slightlynegative with respect to the cathode 16. The resulting anode currentflowing in the wire I I! and through the resistor Illl results in asubstantial voltage drop across the said resistor, thereby reducingsubstantially the potential on the screen grid 105 of the vacuum tube66, and this results in the tube 86 being positively renderednon-conducting. The anode current flowing in the wire I l 1 passesthrough the clutch, of the powered means 22, which is connected with theterminals 26 and 21, thereby energizing the said clutch and resulting inthe shaft 25 being rotated in a counterclockwise direction. Suchrotation swings the arm 32 to the right, enabling the contact arm 38 ofthe anticipator device to separate from the stationary contact 39thereof and causing the anticipator resistor to be included in theenergizing circuit for the coil =44. Such inclusion of the anticipatorresistor 53 results in a reduction of current in the equivalent coil 44to a 400 F. change of temperature of the thermocouple l1, and thereforethe contact arm 45 of the instrument relay 43 swings quickly to the leftand again engages the stationary contact 46. Upon this occurring thecycle of operations described above is repeated and therefore thecontrol device is in a continually hunting or oscillating state, and thecapstan 30 is being rotated back and forth in step with the saidoscillations, the movements of the capstan having relatively smallmagnitude. These movements are transmitted to the control valve l8,actuating the latter back and forth rapidly in step with theoscillations of the control device.

It will be seen that the anticipator device when actuated by the forwardrotation of the powered 10 means 22 operates to cause reverse rotationthereof, and the said reverse rotation of the powered means 22 actuatesthe anticipator device so that the latter operates to again causeforward rotation of the powered means.

With the operation as described above a condition of balance is reachedwhereby the temperature of the jet-turbine engine In is maintainedwithin a predetermined range approximately plus and minus 10 F. or less,the particular predetermined range being determined by the average ofthe values of the current flowing in the instrument relay coil 44 due tothe E. M. F. of the thermocouple H and cutting in and out of theanticipator resistor 53, this average current value in turn beingdetermined in part by the throttle resistor 5| in the thermocouplecircuit.

For such condition of balance a predetermined relation Will existbetween, on the one hand, the temperature of the jet-turbine engine I!)and, on the other hand, the average energization of the instrument coil44 (average of peak and low current values effected through inclusionand exclusion of the anticipator resistor 53), and the coil 44 will beenergized on an average proportionately with the temperature of theengine. That is, for a condition of balance of the control device, ifthe engine temperature should increase for some reason the averagecurrent passing through the coil 44 will increase, and vice v'ersa.Also, a predetermined relationship exists between the temperature of theengine It and the period of oscillation or hunting of the contact arm 45of the instrument relay 43, and also the period of the other oscillatingparts of the control device, inasmuch as the period of oscillation isalso proportionate with the temperature of the engine H). For example,if the temperature of the engine Hi should be increased by somecircumstance not involved with a change of the setting of the controldevice, the coil 44 of the instrument relay 43 would receive moreaverage current and produce greater reactions on the instrument field,and consequently the movements of the contact arm 45 thereof to theright or away from the stationary contact 45 would have a greatermagnitude. Due to the inertia of the contact arm and damping thereof,this would accordingly result in the period of oscillation beingincreased, and in the same manner the period will be decreased ifthrough some circumstance the temperature of the engine l0 were reduced.Of course, a rise in the temperature of the engine Ill and an increasein the period of oscillation of the contact arm 45 would result in thesaid arm being out of engagement with the stationary contact 46 forlonger intervals of time, and therefore the capstan 30 of the poweredmeans 22 would be caused to creep in one direction 1. -e.,counterclockwise, thereby resulting in a closing of the fuel controlvalve 5'6, and this will in turn result in the temperature of the enginebeing reduced. By this action the temperature of the engine isautomatically held within a predetermined range.

From the above it is seen that the amplitude of oscillation of thecontact arm 45 of the instrument relay 43, and of the other oscillatingparts of the control device are proportionate with the temperature ofthe engine It, and for a given setting of the control device, thisamplitude has a predetermined relationship to the said temperature.Also, it will be understood that the oscillation of the contact arm 45is caused by the application of a uni-directional fluctuating deflectingforce to the said arm through the medium of the coil 44, and that theaverage magmtude of the said deflecting force is proportionate with thetemperature of the engine I0. The contact arm 45 is in fact adeflectable member and is biased by means of the usual spiral coilsprings commonly employed in instrument movements, though no such coilsprings are shown in the drawing since their construction and operationare well-known and understood.

Durin normal operation of the control device, at all times when a stateof balance is reached, the average energization of the coil 44 andaverage deflecting force on the coil and on the contact arm 45, and theamplitude and period of oscillation of the coil and arm, and of theshaft and capstan of the device will be within related predeterminednarrow fixed ranges.

If now the throttle lever lei is shifted downward, as viewed in Fig. 1,toward its closed position, less resistance will be included in thethermocouple circuit, and the average current passing through the coil44 will be increased. This will upset the state of balance of thecontrol, and when balance is again established, will result in a newrelationship between the temperature of the engine If), on the one hand,and on the other hand the normally constant factors including theaverage energization of the coil 44 and period of oscillation of thecontact arm and of the other oscillating parts of the control device.The new relationship will be characterized by a new and lower value oftemperature and speed or power of the engine in, and will be effectedthrough closing of the fuel valve E6 in the followin manner: Upon thethrottle lever l3! being shifted downward, as stated above, the saidnormal state of balance is disturbed, and due to the increased averagecurrent flowing through the coil 44 the impulses transmitted to the coiland to the contact arm 45 will be of greater magnitude, and consequentlythe amplitude of oscillation of the contact arm 45 will be greater. Thiswill result in the intervals of operation of the vacuum tube 65 beinglonger than the intervals of operation of the vacuum tube 66, and willcause the shaft 25 and capstan 30 of the powered means 22 to creep in acounterclockwise direction, thereby closing the fuel control valve l6and reducing the temperature and speed of the engine ill. When thetemperature of the engine I!) has been sufficiently reduced so that theperiod of oscillation of the control device has returned to its fixedrange, which is normally constant, a state of balance again will havebeen reached and the engine temperature and power will therefore bemaintained at the new lower value, or to be more exact, within a lowerrange which in practice has a total spread somewhat less than 20 F.

Stated another way, the closing of the throttle lever l3l (moving itdownward) increases the length of the intervals of disengagement of thecontact arm 45 and stationary contact 46, and increases the length ofthe intervals of inclusion of the anticipator resistor 53 in the circuitof the relay coil 44, this being due to the increase in the averageforce on, or driving the contact arm 45.

Conversely, if the throttle lever It! should be shifted upward towardits open position, as viewed in Fig. l, more resistance will be includedin the thermocouple circuit for the instrument relay 43 and the coil 44thereof will have its average current reduced. This again will alter therelationship between the temperature of the engine In on the one handand on the other hand the average energization of the coil 44, and theamplitude and period of oscillation of the contact arm 45. The arm 45and coil 44 will now have a weaker fluctuating force transmitted tothem, and the amplitude of oscillation will be decreased and the perioddecreased.

In consequence of this the intervals of operation of the tube 66 will belonger than the intervals of operation of the vacuum tube 65, thereforethe shaft 25 and capstan 30 of the powered means 22 will be caused tocreep in a clockwise direction thus opening the fuel control valve It.This in turn will cause more fuel to be delivered to the engine Ill andwill increase the temperature and power of the latter, and such increasewill continue until a state of balance is again reached wherein theperiod of oscillation of the control device has returned to its normalfixed value. Thus an automatic control of engine temperature and poweris had whereby these variables may be maintained in any selected one ofa plurality of different predetermined ranges as dgtermined by thesetting of the throttle lever It will be seen that the powered means 22is actuated either forwardly or in reverse direction according towhether the magnitude and period of oscillation of the contact arm 45 isgreater or less than a predetermined value which corresponds with thepredetermined fixed period of oscillation obtained when the controldevice is in a state of balance.

By providing the graduations I32 for the throttle lever l3l, and byaffixing proper values to the graduations, the setting of the throttlelever will be indicative of the temperature of the engine ill within forexample, approximate- 1y plus or minus 10 F.

The oscillating control device of this invention as described aboveprovides for rapid response to changes in the temperature of the engineII] or the setting of the throttle lever I 3| and therefore a closeregulation is had which minimizes the possibility of engine racing ortemperature overshooting or reaching an excessive, dangerous value atany time. For example, a time lag of approximately 15 seconds existsbetween a change in the temperature of the engine ill and the responseof the thermocouple I! to the said change. However, by the provision ofthe anticipator device by which the control is made to have a rapid rateof oscillation the overall response time of the control, or timerequired to establish a given engine temperature, is reduced to about 2seconds, and this is effected as follows. If the throttle lever [31 isshifted upward toward open position, thereby increasing the resistancein the thermocouple circuit connected to the instrument relay 43, animmediate decrease in the average current flowing in the coil 44 of therelay will occur, and if the anticipator device comprising the resistor53 and cooperable contacts 38 and 39 controlling the said resistor wereomitted, the contact arm 45 of the instrument relay 43 would rest for arelatively long interval of time against the stationary contact 45, andthis would result in a long interval of operation of the vacuum tube 66and cause a considerable clockwise rotation of the capstan 3|], therebyopening the fuel valve It by a substantial amount. This in turn wouldfeed a great deal of fuel to the engine In and would result in anexcessive temperature and power thereof, and such temperature and powerwould not be immediately checked, due to the slow response of thethermocouple I'I. However, by the provision of the anticipator device,immediately upon the contact arm 45 engaging the stationary contact 46in the instrument relay 43, the initiation of movement of the capstan 30by such engagement will cause the contact arm 38 of the anticipator toengage the stationary contact 39 thereof, thereby shorting-out theanticipator resistor 53 and resulting in a substantial increase ofcurrent through the coil 44. This substantial increase in currentimmediately drives the contact arm 45 of the instrument relay away fromits cooperable contact 46, and the above will be repeated continually;therefore a condition will not exist where the fuel valve I6 isinitially opened a substantial and excessive amount. Instead, the valveI6 is caused to have a delayed action, so to speak, which approaches thedelayed action or lag of the thermocouple I1 and offsets the effect ofthe latter, and therefore overshooting of the engine temperature iseffectively prevented, and an engine response and reestablishment of acondition of balance is obtained in response to a change in the throttlesetting I3I which is on the order of 2 seconds in spite of the secondtime lag of the thermocouple I1.

It will be noted that the action of the anticipator device comprisingthe resistor 53 and contacts 38 and 39 controlling the said resistor isto continually and rapidly change an unvarying relationship which, ifthe anticipator device were omitted, would exist between on the one handthe temperature of the engine It and on the other hand the energizationof the coil 44, thereby to provide a fluctuating energization of saidcoil. When the anticipator resistor 53 is included in the circuit itresults in a change approximately equal to a 400 F. change oftemperature of the thermocouple IT as above mentioned.

The inclusion of the resistor 53 in the circuit of the coil 44 altersthe relationship which exists between energization and deflection of thecoil and the temperature of the engine II] when the anticipator contacts38 and 39 are engaged and the resistor is short-circuited. Suchinclusion of the resistor 53, effected by small closing movement of thevalve I6, causes an actuation of the powered means 22 in the same senseas and prior to the actuation it would normally have in responding to adrop in temperature of the engine I0 caused by a greater closingmovement of the valve IS.

The net effect of the anticipator means comprising the resistor andcontacts 38 and 39 is thus to decrease the period of hunting oroscillation of the control device, that is, to make it oscillate or huntat a much more rapid rate than that which it would normally have if theanticipator mechanism were not provided. For such event the controldevice would hunt at a relatively slow rate, and the temperature of theengine I0 would fluctuate between relatively wide limits due to the timelag of the thermocouple I1.

However, the anticipator device considerably reduces or narrows therange Within which the engine 59 is maintained, and makes for a muchmore accurate control and one which is more quickly responsive andmaintains engine temperatures within safe limits.

If the control device should be so operated that the valve I6 is drivento one extreme or the other of its movement by the capstan the cam H6 isso arranged that it will actuate one or the other of the limit switchesH2, H3, the said switches opening the circuit of the clutch which isbeing operated to drive the capstan toward the said limiting position,and therefore driv ing force is removed from the capstan, preventingdamage to the mechanical driving system in volving the fuel valve I5 andthe capstan and also the clutch of the powered means 22. The limitswitches H2 and H3 do not interfere with return movement of the capstan30 from the said limiting position but merely relieve the capstan of itsdriving force when it is at said position, and normally when a limitswitch is operating it renders ineffective that part of the operatingcycle of the contact arm which tends to advance the capstan 30 beyondthe limiting position thereof, the limit switch however supporting theoscillation of the control device in much the same manner as the contactarm 45 supports the said oscillation.

The instrument relay 5? has its stationary contact so adjusted that thecontact arm 59 will be disengaged therefrom only upon the movable coil58 being energized with a relatively heavy current, corresponding to adangerously high temperature of the thermocouple I1 and engine I0.Therefore, when the engine reaches such a dangerously high temperaturethe circuit between the wires 12 and 69 will be automatically opened,and the vacuum tube 65 automatically made conducting thereby to causeoperation of the clutch of the powered means 22 connected with theterminals 26 and 21 to cause counterclockwise rotation of the shaft 25and to close the fuel valve I6. This, therefore, is a safety device bywhich excessive temperatures of the engine I0, which might damage theengine, are automatically prevented. If the engine should approach suchexcessive heating and should thereafter become cooled to a safertemperature the response of the thermocouple I! will enable the contactarm 59 of the instrument relay 51 to again engage the stationary contact60 thereof whereupon the automatic control of the engine temperature isreestablished through functioning of the instrument relay 43.

While the blocking relay unit 56 comprising the vacuum tubes and 66 isshown as having both screen grids connected for blocking purposes, theconnection to the screen grid I05 of the tube 56 may be omitted and thecircuit constants altered to obtain a suitable alternate operation ofthe tubes.

The rotary selector switch H9 is so arranged that it may be shifted toan off position, as indicated, whereupon the wires I29, II! and H8 arerespectively disconnected from the wires I21, I20 and I2I, in whichevent the automatic control over the engine temperature is discontinued.For such setting of the switch H9 the fuel valve I6 will remain in theposition it occupied at the time that the switch was shifted to offposition.

Means are also provided under the control of the selector switch H9 formanually regulating the fuel valve IS without benefit of automaticregulation. This means comprises a pair of push button switches I40 andM! which are operable by means of push buttons I42 and I43 respectively.

The switch I49 is a double pole single throw switch normally biased toopen position and comprises a pair of blade contact arms I44 and I45which are insulated from each other and are actuated by operation of thepush button I42.

For cooperation with the movable blades I44 and I45 stationary contactblades I46 and I41 are provided. The switch I4I is also a double polesingle throw switch normally biased to open position, and comprises apair of movable contact blades I48 and I49 insulated from each other andactuated by operation of the push button I43. For cooperation with theblades I48 and I49 stationary contact blades I50 and II are provided.

Connections for the switches I40 and MI are as follows: The contactblade I46 is connected by a wire I52 with the contact blade I48, and thesaid wire I52 is connected by a wire I53 with the wire I29 of thecontrol device. The contact blade I41 is connected by a wire i54 withthe contact blade I5 I, and the wire I54 is connected by means of aresistor I55 (which may be of approximately 10,000 ohms resistance), toa ground connection I56. The contact blade I44 is connected by a wireI51 to the contact blade I50, and the latter is connected by a wire I56with the selector switch Il9 so that when the selector switch is inmanual position the wire I56 is connected to the wire I21. The contactblades I45 and I49 are respectively connected by wires i539 and I60 withthe selector switch I I9 so that when the latter is in manual positionthe wires I59 and I60 will be respectively connected with the wires Iand I2 I.

When the selector switch H9 is in manual position the wires I29 and H1and H8 are disconnected from the wires I21, I26, I21 respectively sothat automatic control of the engine is not had. Also for this settingof the selector switch H9 if the push button I42 is depressed the clutchof the powered means 22 connected with the terminals 26 and 21 isenergized from the high voltage coil 94 of the power transformer 19through the resistors I55 and IN, and the shaft and capstan of thepowered means 22 is caused to rotate in a counterclockwise direction,closing the valve 16. If the push button I43 is depressed, the clutch ofthe powered means 22 which is connected with the terminals I28 and I29is energized through the resistors I and I00 from the high voltagewinding 94 of the transformer 19 and the shaft 25 and capstan 30 arecaused to rotate in a clockwise direction, opening the valve I6.

For such manual operation of the valve I6 the anticipator mechanismcomprising the anticipastor resistor 53 and contacts 38 and 39 of coursedo not have any effect on the actuation of the valve.

For the purpose of indicating whether or not the motor of the poweredmeans 22 is energized, an indicator light I6I is provided, connected bya wire I62 with the wire I24, and by a wire I63 with the wire I25.

In accordance with the invention means are provided in conjunction withthe oscillating control device whereby the effect, on the engine I0, ofconditions such as sudden diving or steep climbing of the aircraft isautomatically minimized, by immediately supplying the engine with eitherless fuel or more fuel respectively, this being done during the briefinterval in which the change in the speed of the aircraft is occurring.That is, if the aircraft should suddenly be thrown into a steep climb,the engine I0 will automatically immediately be fed more fuel, beforethe pilot of the craft can respond to the climb by advancing thethrottle. Also, if the aircraft should be thrown into a sudden dive, thefuel to the engine I0 will be immediately automatically 16 decreased,and this will occur before the pilot has time to decrease the throttlesetting. Such sudden changes of the aircraft may be occasioned, forinstance, by airpockets or bumpy air conditions.

Accordingly, referring to Fig. 1, a relay I64 is provided havingcontacts I65 and I66 respectively connected by wires I61 and I68 to thewire 50 and contact arm I30 of the throttle resistor 5I. The contactsI65 and I66 are normally open, and therefore the functioning of thethrottle resistor 5| is normally not altered. The relay I64 has a coilI69 connected by a wire I10 with a coil I1I of the relay I35, and thewire I10 is connected to one terminal of a D. C. generator I12 which iscoupled to be driven from the driving shaft I4 of the engine III, asindicated by the broken line I13. The other terminal of the generatorI12 is connected to a condenser I14 whose other terminal is connected toa wire I15 the ends of which are connected respectively to rectifierunits I16 and I11. The rectifier I16 is connected by a wire I18 with therelay coil I69, and the rectifier I11 is connected by a wire I19 withthe relay coil I1I. The rectifier I16 is arranged to enable current toflow through it from the wire I18 to the wire I15, and to preventcurrent from flowing through it from the wire I15 to the wire I18. Therectifier I11 is arranged to enable current to flow through it from thewire H5 to the wire I19 and to prevent current from flowing through itfrom the wire I15 to the wire I19.

In conjunction with this organization the propeller I5 of the aircraftis preferably chosen to be of the variable pitch type, and the pitch ofthe propeller is adjusted in conjunction with shifting of the throttlelever I3I so that the driving shaft I4 of the motor I0 has asubstantially constant speed for different throttle settings anddifferent fuel inputs to the engine.

The operation of this automatic control responsive to sudden climbing ordiving of the aircraft is as follows: During normal flight conditions ofthe craft, the engine shaft I4 will be rotating at a substantialconstant speed and the output of the D. C. generator will have a fixedand unvarying value. For such value no current will be caused to flow ineither of the relay coils I69 or I1I. If however the aircraft should becaused to suddenly dive, as by an atmospheric condition, the engineshaft I4 will suddenly increase its speed, and this will increase theoutput voltage of the generator I12 and cause a current to flow throughthe generator I12, relay coil I69 and rectifier I16, and through thecondenser I14. Such current will only continue to fiow as long as anacceleration of the engine shaft I4 and generator I12 takes place.Energization of the relay I64 caused by such current will close therelay contacts and result in the throttle resistor 5i beingshortcircuited, thereby increasing the current through the instrumentrelay coil 44 and causing the contact arm 45 thereof to separate fromthe stationary contact 46. This will immediately render inoperative thevacuum tube 66 and cause the vacuum tube 65 to become operative, withthe result that the powered means 22 will be caused to operate in acounterclockwise direction, thereby Partly closing the fuel valve I6 andreducing the fuel supply to the engine I0. As soon as acceleration ofthe engine shaft I4 and generator I12 ceases, the relay I64 will bedeenergized due to the condenser I14 becoming 17 fully charged and notpassing any more current.

A similar action occurs if the aircraft should suddenly be made toclimb, as by an atmospheric condition, since deceleration of the engineshaft I4 will cause a drop in voltage at the terminals of the generatorI12, which will result in current flowing through the relay coil I'II,rectifier Ill and condenser I14 by discharge of the latter. Such currentwill open the contacts of the relay I35 and cause the full resistancevalue of the throttle resistor 5| to be included in the thermocouplecircuit, thereby reducing the energization of the coil 44 and causingthe contact arm 45 of the instrument relay to remain in engagement withthe stationary contact 48. This will cause the vacuum tube 68 to becomeoperative and will actuate the powered means 22 in a clockwisedirection, opening the fuel valve I9 and increasing the fuel supply tothe engine I automatically.

It will be noted that the quick automatic increase and decrease of flowof fuel to the engine I0 in response to climbing or diving of theaircraft is effective only during deceleration and acceleration of theengine shaft I4, and as soon as such change in speed of rotation ceasesthe automatic compensation for the change ceases. This organization istherefore operative before the pilot of the aircraft has time toreadjust the setting of the throttle I 3I, and by the time the automaticcompensation ceases to operate the pilot will have been able to properlyreset the throttle I3I if this should be necessary. Often it will not benecessary due to the altered flight conditions of the aircraft beingonly temporary.

Another form of invention is illustrated in Fig. 2. In this figure partswhich correspond to parts in Fig. 1 have been given the same characters,generally. The operation of this form of the invention is in manyrespects similar to the operation of the form shown in Fig. 1, and ingeneral the following structural diiferences exist between the two formsof the invention: Instead of the pair of vacuum tubes 55 and 96, thedevice of Fig. 2 employs but a single vacuum tube, and employsmechanical relays which are not of the sensitive-instrument type. Asecond sensitive-instrument relay for safeguarding the engine againstextremely high temperatures is not shown in the device of Fig. 2,although it may be incorporated therein in the same manner as in thedevice of Fig. 1. Instead of a single anticipator resistor as shown inFig. 1, the device of Fig. 2 incorporates two anticipator resistors, onecontrolled by the powered means of the device and the other controlledby the above mentioned mechanical relays. Finally, a slightly differentform of powered means for actuating the fuel control valve of the engineis illustrated.

Referring to Fig; 2, propeller I5 of the jetturbine engine I0 is shownin full lines, the engine I9 being shown in block outline for the sakeof simplicity of illustration. Responsive to the heating of the engineI0 is the thermocouple I'! which is shown in schematic representation.

The powered means for driving the fuel valve I6 which controls the fuelsupply to the engine I0 is shown as comprising an electric motor I84having an armature I85 and a field I89, the armature shaft carrying apulley I81 over which a belt I88 passes. The belt I88 is guided by idlerpulleys I89 and I90 and passes over pulleys I9I and I92 which areloosely carried on a shaft I93. The belt I88 also passes over a thirdidler pulley I94 by which it is enabled to drive the pulleys I9I and I92in opposite directions. A clutch plate I95 is fixedly mounted on a shaftI93 between the pulleys I9I and I92 and is cooperable with clutchfacings I96 and I9! whereby the shaft I93 may be driven in one directionor the other upon its being axially shifted to either of two positions.

Axial shifting of the shaft I93 is accomplished by a forked arm I98engageable with collars 299 and 200 on the shaft I93. The arm I98carries a magnetic armature piece 20I which is subjected to magneticattraction from a core 232 energized by a magnet coil 203. An extensionspring 204 connects the arm I98 with a stationary anchorage 205 andnormally holds the armature piece 20I away from the core 202 when thelatter is not magnetized.

The shaft I93 carries a pinion 208 meshing with a gear wheel 20? mountedon and driving shaft 25 which carries the capstan 30 and which ismechanically connected to drive the fuel valve The anticipator devicecomprises arm 32 which is frictionally carried by the shaft 25 and isengageable with abutment M and with switch arm 38 to actuate the latter.The switch arm 38 is engageable with the abutment or stop 40 and withthe stationary contact 39. The contact arm 38 and stationary contact 39are connected re-' spectively by wires 208 and 209 through a connectorfitting 2I0 with wires 2 and 2I2, the latter Wire being connected to oneend of an anticipator resistor 2I3. Also, a second anticipator resistor2I4 is provided, connected by a wire 2I5 to the wire 2'08 and by a'wire2 I6 to the wire 209.

In Fig. 2 the throttling control and automatic safety control responsiveto sudden climb and diving of the aircraft are blocked off by a brokenrectangular outline 2H, and the parts illustrated within said outlineare numbered similarly to corresponding parts in Fig. l, and functionsimilarly thereto.

The thermocouple I! is connected by a wire 2 I8 with the movable coil2l9 of a sensitive instrument relay 220 which isin general similar tothe relays 43 and 51, the other end of the coil 2I9 being connectedthrough a resistor 22I to a wire 222 which connects through a connectorfitting 223 and a wire 224 to one end of the throttle resistor 5!. Theremaining terminal of the thermocouple I! is connected by a wire 225through the fitting 223 with the wire 2I I.

The instrument relay 220 has a contact arm 226 which is cooperable witha stationary contact 22?, the latter being connected through a resistor228 (which may beof one megohm resistance) to a wire 229 which in turnconnects to one end of a grid resistor 230 (which may be ofapproximately three megohms resistance) the other end of said resistor230 being connected with the control grid 23I of a screen grid vacuumtube 232. The contact arm 22 6 of the instrument relay is connected by awire 233'with one end of the heater 234 of the vacuum tube 292 (whichmay be of type 9003, the other end of the said heater being connectedwith the cathode 235 of the vacuum tube and the cathode beingconnectedto one end of a resistor 236 (which may be of approximatelythirty ohms resistance). The other end of the resistor 236 is connectedto a wire 23? which connects with a grid leak 238' and grid condenser239 the other ends of which'are connected to the wire 222. The leak 23!and condenser 23s may be of twenty megohms resistance and .001 mid.capacity respectively.

Energization of the device of Fig. 2 is supplied by a battery 2% whichmay have a voltage of 2d, the negative terminal of which battery isconnected to a negative line wire 24! in turn connected with the wire23'!. The positive terminal of the battery 24!) is connected by a wire222 with a multi-pole selector switch 243 having three positions asindicated, off, M (for manual operation) and A (for automatic operationof the device). When the selector switch 243 is set for automaticoperation the positive supply wire 2 52 thereof is connected with a wire242 leading from the switch and through the connector fitting 223 forconnection with a wire 245 which is in turn connected to one end of thecoil 246 of a relay 2277, the other end of the coil being connected by awire 243 with the anode 249 of the vacuum tube 232. The relay coil 2:31is bridged by a condenser 256 to prevent its chattering.

The screen grid 25! of the vacuum tube 232 is connected by a wire 252with a resistor 253 (which may be of 100 ohms resistance), the saidresistor being also connected by a Wire 25% with the wire 233.

The relay 24'! has an armature contact 255 connected by a wire 256 withthe wires 245 and 252, said relay controlling the energization of threerelays 257, 258 and 259, and for this purpose the coils 25b, 26! and 262of the said three relays are connected in parallel by wires 2% and 26 i,and the wire 253 is connected by a wire 2% through the connector fitting223 to a wire 2% which connects with the stationary contact Ziil of therelay 241. The wire 264 connected with the relay coils 26G, 26! and 262is energized through connection with a Wire 2268 which is connected withthe negative supply wire 2M.

For the automatic setting of the selector switch 243 the wire 244thereof is connected to wires 269 and 270, the wire 262 being connectedthrough a connector fitting 279 with a wire 222 leading to the armature!85 of the motor !34. The other terminal of the armature M is connectedby a wire 2'53 through the connector fitting 27! to a wire 214 whichleads to the selector switch 243 and which, when the switch is inautomatic setting, is connected with a wire 215 in turn connectedthrough the fitting 27! with a wire 27ft joining to one end of the motorfield M36. The other end of the motor field is connected by a wire 27'!through the fitting 2H with the negative supply wire 24! of the circuit.

The wire 2!!! leading from the selector switch 243 connects with aresistor 2l8 (which may be of ohms resistance), the said resistor eingconnected by a wire 279 through the fitting 2H to a wire 2263 whichconnects with a normallyclosed limit switch 28!, the said switch beingalso connected by a wire 282 with the magnet coil 203 for actuating thereversing clutch sys tem of the capstan drive. The limit switch 285 isactuated by cam Us on the capstan shaft the switch being opened when thecapstan re and valve !6 approach a limit of movement. The other end ofthe magnet coil 203 is connected by a wire 283 through the fitting 2H toa wire 282 which connects with a contact 285 of the relay 258. The othercontact 285 of the relay 258 is connected by a wire 28'! with a contact222 of the relay 251, and the cooperable contact 289 of said relay isconnected by a wire 2% with the wire 264.

Sparking of the contacts of the relays 25! and 252 is reduced by aresistor 29! and condenser 292 connected with the wires 264- and 284,and sparking at the contacts 255 and 26'! of the relay 252 is reduced bya resistor I82 and condenser I83 connected across said contacts.

The anticipator circuit of the device is completed by wires 293 and 294which connect the ends of the anticipator resistor 2l3 respectively withcontacts 295 and 296 of the relay 259, and the relay contact 295 is alsoconnected by a wire 22'? with the wire I31.

Considering the capstan 30, a second limit switch 298, which is normallyopened, is located for actuation by the cam !!6 when valve !6 reachesthe other limit of movement. The limit switch 298 is connected by a wire229 through the connector fitting 27!! with the negative supply wire 22!of the circuit, and the switch 298 is also connected by a wire 300 tothe wire 283.

Arcing of the contacts of the limit switch 28! is minimized by a seriesconnected resistor 30! and condenser 302 which are respectivelyconnected by wires 363 and 304 with the wires 280 and 282.

A signal lamp 305 is connected to the wire 215, and is connected througha resistor 306 with the negative supply wire 24!, thereby to indicatewhen the motor I84 is being energized.

Operation of the device of Fig. 2, with the selector switch 243 set inautomatic position, is as follows: Assuming that the engine It isrunning, and that the thermocouple I! is heated by the engine, andassuming that the vacuum tube 232 has been suitably warmed up, and withthe contact arm 226 of the instrument relay 220 in the position shown(disengaged from the stationary contact 22?), the vacuum tube 232 willbe in a non-conducting condition. This is because the control grid 23!of the tube is negative with respect to the cathode 235, since thecontrol grid is connected through the grid leak and resistor to thenegative line wire 24! whereas the cathode is connected between theheater 234 and drop resistor 226 so as to have a positive potential withrespect to the negative wire 24!, equivalent to the voltage drop acrossthe resistor. By virtue of this, the relay 28'! will be deenergized andthe contacts 255 and 26'! will be in engagement as shown. This willcause the three relays 251, 258 and 259 to be energized. The contacts ofthe relays 25? and 258 will be closed, thereby to establish a circuitfrom the negative side of the battery 24%] through the contacts andwires 284 and 283 to the magnet coil 203, and the said coil will beenergized by virtue of its connection through the wire 282, limit switch23! and wire 282, and through the wire 219, resistor 278 and wire 212 tothe positive supply wire 242 from the battery, the connection betweenthe wires 210 and 222 being effected through the selector switch 222.Energization of the magnet coil 203 will cause the clutch disk to engagethe clutch facing 892, thereby to rotate the shafts I93 and .5 so as toclose the fuel valve !6, the rotation of the shaft 25 being in acounterclockwise direction for effecting this, as viewed in connectionwith the driving arm 32 which operates the anticipator switch arm 38. Anopen condition of the anticipator switch contacts 38 and 39 will causethe anticipator resistor 2 !4 to be included in the circuit by which theinstrument relay coil 2!!! is energized. Also energization of the relay259 will cause the contacts thereof to be opened, thereby causing thesecond anticipator resistor 213 to be included in the energizing circuitfor the instrument relay 219. The result of inclusion of these twoanticipator resistors 213 and 214 in the energizing circuit for theinstrument relay coil 219 will result in a sharp decrease in the currentpassing through the coil, and such decrease will cause the deflection ofthe coil and the contact arm 226 controlled thereby to decrease, therebyresulting in engagement of the contact arm 226 and stationary contact221. Such action will immediately produce a positive potential on thecontrol grid 231 of the vacuum tube 232, inasmuch as the wire 233 has apositive potential approximately to equivalent of the voltage dropexisting across the resistor 246 and heater 234. The vacuum tube 232therefore becomes operative, causing energization of the relay 247 anddeenergization of the three relays 251, 258 and 259. This in turn causedeenergization of the magnet coil 203, and results in the clutch disk:95 being shifted out of engagement with the facing 19? and intoengagement with the facing 19%. This reverses the rotation of the shafts193 and 25, the latter now rotating clockwise and opening the valve 15and causing the driving arm 32 to actuate the anticipator switch arm 33and cause the latter to engage the stationary contact 39 of the switch.Closing of the anticipator switch contacts and deenergization of therelay 259 causes a short-circuiting of the anticipator resistors 214 and213, and results in an immediate substantial increase in theenergization of the coil 219 of the instrument relay 220. The abovecycle or operations is continually repeated, the device thereby being ina state of oscillation or hunting, in a manner similar to the device ofFig. 1, and a state of balance is reached whereby the position of theslider contact 130 on the throttle resistor 51 is the controlling factorin the temperature and speed of the engine 10. As in the case of thedevice of Fig. 1, the period of oscillation and magnitude of movement ofthe oscillating parts, for a given position of the throttle lever 131,will have a given predetermined relation to the temperature of theengine 10, and changes in the setting of the throttle lever [31 willchange this relation. Such change will at first be reflected in a changein the period and magnitude of oscillation of the components of thecontrol device, the said period and magnitude of oscillation graduallyreturning to its predetermined value however as the temperature andspeed of the engine 10 are altered, and the changed relation ultimatelywill therefore be due solely to a change in the temperature and speed inthe engine.

When the selector switch 243 is in the 01f position, the wires 242, 214,269 and 2'10 connected therewith are left open-circuited, and since thewire 242 is the sole positive supply line of the circuit, the entirecontrol device will be rendered inoperative and the fuel valve 16 willremain in the position it had when the selector switch was switched tooff position.

For manual operation of the control device a pair of push buttonswitches 30'! and 308 is provided. The switch 301 has movable contactarms 3% and H which are normally engaged with stationary contacts 311and 3,12 respectively, and which may be spread apart by depressing themanually operable button 313 so as to cause them to respectively engagestationary contacts 314 and 355. The switch 308 has a pair of contactarms H6 and 311 which are normally respectively engaged with stationarycontacts 318 and 319 and which may be spread apart by cle-- pressing amanually operable button 320 to cause them to respectively engagestationary contacts 321 and 322. Contacts 315 and 318 of the switch areconnected by a wire 323, contacts 312 and 322 connected together by awire 324, contacts 31 and 319 connected together by a wire 325, andcontacts 311 and 321 connected by a wire 326. The contacts 309 and 3!!are connected by wires 32'! and 328 to the selector switch 243 so thatwhen the latter is set for manual operation these wires will berespectively connected with the wires 242 and 269. The contact 316 ofthe switch 309 is connected by a wire 329 with the selector switch 243so as to be connected with the wire 274 when the switch is in manualoperation. For such position of the switch, automatic operation of themagnet coil 203 will be prevented by virtue of the fact that the wire210 leading from the switch is not connected with the positive side ofthe battery, due to the switch open-circuiting the said wire; the wire2'10 is depended on by the magnet coil 203 for its positive connectionwith the battery 240. Instead, the clutch disk will be held by theextension spring 204 in engagement with the clutch facing 196continuously, and the motor 184 may be energized for rotation in onedirection or the other by depressing one or the other of the buttons 313and 329 of the pair of switches 30'! and 308, the said switches actingas motor reversing switches as may be seen by following out thesecircuits.

While the control device of the present invention is applied to ajet-turbine engine to control the temperature thereof, it should beunderstood that the device may be applied to other instrumentalities orvariables to control the values thereof, the intended scope of theinvention being defined in the appended claims.

Variations and modifications may be made within the scope of thisinvention and portions of the improvements may be used without others.

I claim:

1. The method of maintaining within a predetermined range a variableregulated by a reversible control, which includes the steps of applyingto a biased defiectable member a uni-directional fluctuating deflectingforce of an average magnitude proportionate with the value of thevariable to cause oscillation of the member, and operating saidreversible control in one direction or the other according to. whether-ie magnitude of oscillation of the member is, greater or less than apredetermined value corresponding to the said predetermined range ofthevariable.

2. The method of maintaining within a predetermined range a variableregulated by a reversible control, which includes the steps ofautomatically applying to a biased deflectable member when and only whenthe latter is in predetermined position of low deflection, a deflectingforce of a magnitude proportionate with the value of the variable tocause oscillation of the member, automatically operating said control inone direction whenever the member is out of said predetermined position,and operating the control in the other direction whenever the member isin said predetermined position.

3. The method of maintaining a variable within a predetermined range bya reversible control, which includes the steps of continually moving amember away from and back to a predetermined fixed position to have amagnitude. of

23 movement proportionate with the value of the variable, andoscillating said control to shift the center point of its movement inone direction or in the other according to whether the magnitude ofmovement of the member is greater or less than a predetermined valuecorresponding to the said predetermined range of the variable.

4. The method of maintaining a variable within a predetermined range bya reversible control, which includes the steps of continually moving amember back and forth between retracted and advanced positions to have amagnitude of movement proportionate with the value of the variable, andautomatically operating said control in one direction or the otheraccording to whether the magnitude of movement of the member is greateror less than a predetermined value corresponding to the saidpredetermined range of the variable; and manually varying the magnitudeof movement of said member to affect a selection of a new predeterminedrange for said variable.

5. The method of maintaining within a predetermined range a variableregulated by a reversible control, which includes the steps ofcontinually moving a member back and forth between a predeterminedretracted position and advanced positions with a magnitude of movementproportionate with the value of the variable, and moving said control inone direction or the other according to whether the member isrespectively in or out of said retracted position, the control beingmoved more in one direction than in the other when the magnitude ofmovement of the member is greater than a predetermined value, and beingmoved less in one direction than in the other when the magnitude ofmovement of the member is less than a predetermined value.

6. The method of maintaining a variable within a predetermined range bya reversible control, which includes the steps of producing in aforce-transmitting medium a uni-directional force having a magnitudeproportionate with the value of the variable, periodically altering theeffectiveness of the force so as to provide oscillations in said mediumhaving a period proportionate with the value of the variable, andautomatically operating the control in one direction or the other inresponse to the period of the oscillations being greater or less than apredetermined value corresponding to said predetermined range of thevariable.

7. The method of maintaining a variable within a predetermined range bya reversible control, which includes the steps of producing in aforcetransmitting medium a uni-directional force having a magnitudeproportionate with the value of the variable, periodically altering theeffectiveness of the force so as to provide oscillations in said mediumhaving a period proportionate with the value of the variable,automatically operating the control in one direction or the other inresponse to the period of the oscillations being greater or less than apredetermined value corresponding to said predetermined range of thevariable, and manually altering the effectiveness of the force to selecta new predetermined range for the variable.

8. The method of maintaining within a predetermined range a variableregulated by a reversible control, which includes the steps of producingin a force-transmitting medium a unidirectional force having a magnitudeproportionate with the value of the variable, periodically altering theeffectiveness of the force so as to provide pulsations in said mediumhaving a period proportionate with the value of the variable, andoscillating the control to shift the center point of its movement in onedirection or the other according to whether the period of the pulsationsis greater or less than a predetermined value corresponding to saidpredetermined range of the variable.

9. In a propelled device, the method of maintaining within apredetermined temperature range a jet-turbine engine regulated by areversibly-operable fuel valve, which includes the steps of producing ina force-transmitting medium a uni-directional force having a magnitudeproportionate with the temperature of the engine, periodically alteringthe effectiveness of the force so as to provide pulsations in saidmedium having a period proportionate with the temperature of the engine,and oscillating the fuel valve to shift the center point of its movementin one direction or the other according to whether the period ofpulsations is greater or less than a predetermined value correspondingto the said temperature range.

10. In an aircraft, the method of maintaining within any selected one ofa plurality of different predetermined temperature ranges a jet-turbineengine regulated by a reversibly operable fuel valve, which includes thesteps of producing in a force-transmitting medium a uni-directionalforce having a magnitude proportionate with the temperature of theengine and in predetermined relation thereto, periodically altering theeffectiveness of the force so as to provide oscillations in said mediumhaving a period proportionate with the temperature of the engine,operating the fuel valve in one direction or the other according towhether the period of oscillations is greater or less than apredetermined value, and altering the relation between the period ofoscillations and temperature of the engine to select the temperaturerange the engine is to be maintained 11. Apparatus for maintaining thetemperature of an engine within a desired range, comprising a fuelcontrol valve; means for rapidly moving the fuel valve by minute equalamounts in opening and closing direction while the engine is at thedesired temperature range, and for causing one kind or the other of suchvalve movement to be of greater amount according to whether the enginetemperature drops or rises, to open or close the valve respectively, theperiod of movement of the valve having a predetermined relationship tothe said temperature range; and means for altering the said relationshipto select a new temperature range for the engine.

12. Apparatus for maintaining the temperature of an engine within adesired range, comprising a fuel control valve; means for rapidly movingthe fuel valve by minute equal amounts in opening and closing directionwhile the engine is at the desired temperature range, and for causingone kind or the other of such valve movement to be of greater amountaccording to whether the engine temperature drops or rises, to open orclose the valve respectively, the period of movement of the valve havinga predetermined relationship to the said temperature range; and meansfor automatically temporarily altering the said relationship in responseto sudden decreases or increases in speed of the engine, to respectivelyopen or close the said fuel valve.

13. Apparatus for maintaining the temperature' of an engine within adesired range, comprising a fuel control valve; a movable member; meansfor moving the member back and forth between retracted and advancedpositions to have a magnitude of movement proportionate with thetemperature of the engine; means for operating said fuel valve in onedirection or the other accordingto whether the magnitude of movement ofthe member is greater or less than a predetermined value correspondingto the said temperature range of the engine, the magnitude of movementof the member having a predetermined relationship to the saidtemperature range; and means for altering the said relationship toselect a new temperature range for the engine.

14. Apparatus for maintaining the temperature of an engine within adesired range, comprising a fuel control valve; a closed electricalcircuit; means for introducing a uni-directional E. M. F. in thecircuit, having a magnitude proportionate with the temperature of theengine to cause a current to flow in said circuit; means forperiodically decreasing and restoring to its original value the saidcurrent, so as to produce oscillations having a period proportionatewith the temperature of the engine; and means for oscillating said fuelvalve to shift the center point of its movement in one direction or theother according to whether the period of said oscillations is greater orless than a predetermined value corresponding to the said predeterminedrange of the variable.

1-5. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising an oscillatoryactuator device having means for oscillating said control device toshift the center point of its movement in one direction or the otheraccording to whether the period of oscillation of the oscillatoryactuator device is greater or less than a predetermined value, saidoscillatory actuator device including a sensitive instrument movement,and said oscillatory actuator device being so arranged that failure ofthe sensitive instrument movement to function results in operation ofthe control device to cause the variable to attain a dangerous extremevalue; and safety means, connected with the oscillatory actuator deviceand rendered operative upon the variable approachmg said extreme value,for causing operation of the control device in one direction onlywhereby the variable is prevented from attaining said value.

16. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising an oscillatoryactuator device having means for operating said control device in onedirection or the other according to whether the period of oscillation ofthe oscillatory actuator device is greater or less than a predeterminedvalue corresponding to said predetermined range of the variable, saidoscillatory actuator device including a sensitive electric-instrumentmovement; and means for causing the period of oscillation of saidoscillatory actuator device to be proportionate with the value of thevariable, said means including a pyrometer component acted on by saidvariable and connected to said instrument movement, said oscillatoryactuator device including contact means actuated concurrently with saidcontrol device and connected with said resistor.

1'7. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising an oscillatoryactuator device having a defiectable member and having means foroscillating said control device to shift the center point of itsmovement in one direction or the other according to whether the periodof oscillation of the oscillatory actuator device is greater or lessthan a predetermined value; and means controlling said deflectablemember for causing the period of oscillation of said oscillatoryactuator device to be proportionate with the value of the variable, saidperiod of predetermined value correspoinding to said predetermined rangeof the variable, and said oscillatory actuator device including: apair'of screen grid vacuum tubes and circuits therefor, one of saidtubes having its electrodes polarized to render it normally conducting;and means, controlled by said defiectable member, for polarizing theelectrodes of the other tube to render it either conducting ornon-conducting, said tubes being so interconnected that said one tube isrendered non-conducting whenever the said other tube is conduct- 18. Anautomatic control device for use with a power-producing instrumentalitywhich has a rotary drive shaft connected with a variable load, and whichis regulated by a reversible control device governing an input ofconvertible energysupplying substance to said instrumentality,comprising an oscillatory actuator device having means for operatingsaid control device in one direction or the other according to whetherthe period of oscillation of the oscillatory actuator device is greateror less than a predetermined value; means connected to the oscillatoryactuator device and responsive to and proportionately with convertedenergy of the input to the instrumentality for causing the period ofoscillation of the oscillatory device to be proportionate with the saidconverted energy, said period and energy having a predeterminedrelationship; and means for automatically changing the relationshipbetween said period of oscillation and converted energy in response toacceleration of said drive shaft, thereby to reduce the input ofconvertible energy-supplying substance to the instrumentality, saidpredetermined relationship being automatically reestablished uponcessation of said acceleration.

19. An automatic control device for use with a power-producinginstrumentality which has a rotary drive shaft connected with a variableload, and which is regulated by a reversible control device governing aninput of convertible energysupplying substance to said instrumentality,comprising an oscillatory actuator device having means for operatingsaid control device in one direction or the other according to whetherthe period of oscillation of the oscillatory actuator device is greateror less than a predetermined value; means connected to the oscillatoryactuator device and responsive to and proportionately with convertedenergy of the input to the instrumentality for causing the period ofoscillation of the oscillatory device to be proportionate with the saidconverted energy, said period and energy having a predeterminedrelationship; and means for automatically changing the relationshipbetween said period of oscillation and converted energy in response todeceleration of said drive shaft, thereby to reduce the input ofconvertible energy-supplying substance to the instrumentality, saidpredetermined relationship being automatically reestablished uponcessation of said deceleration.

20. An automatic settable control device for use with a power-producinginstrumentality which has a rotary drive shaft connected with a variableload, and which is regulated by a reversible control device governing aninput of fuel to said instrumentality, comprisin an oscillatory actuatordevice having means for oscillating said control device to shift thecenter point of its movement in one direction or the other according towhether the period of oscillation of the oscillatory actuator device isgreater or less than a predetermined value; means connected to theoscillatory actuator device and responsive to and proportionately withheat from fuel burned in the instrumentality for causing the period ofoscillation of the oscillatory device to be proportionate with the saidheat, said period and heat having a predetermined relationship; settablemeans for changing the predetermined relationship between said period ofoscillation and heat to other predetermined relationships, thereby tochange the input of fuel to the instrumentality; and means forautomatically changing a predetermined relationship between said periodof oscillation and heat to another relationship in response toacceleration of said drive shaft, thereby to reduce the input of fuel tothe instrumentality, said predetermined relationship being automtaicallyreestablished upon cessation of said acceleration.

21. An automatic control device for use with a power-producinginstrumentality which has a rotary drive shaft connected with a variableload, and which is regulated by a reversible control device governing aninput of fuel to said instrumentality comprising an oscillatory actuatordevice having means for oscillating said control device to shift thecenter point of its movement in one direction or the other according towhether the period of oscillation of the oscillatory actuator device isgreater or less than a predetermined value; means connected to theoscillatory actuator device responsive to and proportionately with heatfrom fuel burned in the instrumentality for causing the period ofoscillation of the oscillatory device to be proportionate with the saidheat, said period and heat having a predetermined relationship; andmeans for automatically changing the relationship between said period ofoscillation and heat in response to acceleration or deceleration of saiddrive shaft, thereby to reduce or increase respectively the input offuel to the instrumentality, said predetermined relationship beingautomatically reestablished upon cessation of said acceleration ordeceleration.

22. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptiveinstrument; means for energizing the electro-receptive instrument inresponse to said variable and proportionately with the value thereof; amechanism for operating said powered means in one direction or theotherin response to said instrument being energized respectively less than ormore than a predetermined extent which corresponds to said predeterminedrange of the variable, said mechanism and powered means continuallyhunting; and an anticipator device for decreasing the period of huntingof said mechanism and powered means.

23. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptiveinstrument; means for energizing the electro-receptive instrument inresponse to said variable and proportionately with the value thereof; amechanism for operating said powered means in one direction or the otherin response to said instrument being energized respectively less than ormore than a predetermined extent which corresponds to said predeterminedrange of the variable, said mechanism and powered means continuallyhunting; and an anticipator device for decreasing the period of huntingof said mechanism and powered means, said mechanism including: a pair ofscreen grid vacuum tubes and circuits therefor, one of said tubes havingits electrodes polarized to render it normally conducting; and meanscontrolled by the electroreceptive instrument for polarizing theelectrodes of the other tube to render it either conducting ornon-conducting, said tubes being so interconnected that said one tube isrendered nonconducting whenever the said other tube is conducting.

24. An automatic control device for use with a power-producinginstrumentality which has a rotary drive shaft connected with a variableload, and which is regulated by a reversible control device governing aninput of convertible energysupplying substance to said instrumentality,comprising an oscillatory actuator device having means for operatingsaid control device in one direction or the other according to whetherthe period of oscillation of the oscillatory actuator device is greateror less than a predetermined value; means connected to the oscillatoryactuator device responsive to and proportionately with converted energyof the input to the instrumentality for causing the period ofoscillation of the oscillatory device to be proportionate with the saidconverted energy, said period and energy having a predeterminedrelationship; and means for automatically changing the relationshipbetween said period of oscillation and converted energy in response toacceleration or deceleration of said drive shaft, thereby to reduce orincrease respectively the input of convertible energy-supplyingsubstance to the instrumentality, said predetermined relationship beingautomatically reestablished upon cessation of said acceleration ordeceleration and said means including a pair of circuits, a D. C.electric generator driven from said drive shaft and connected toenergize one of said circuits, and including a condenser charged by saidgenerator and dischargeable through the other of said circuits.

25. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptiveinstrument; means for energizing the electro-receptive instrument inresponse to said variable and proportionately with the value thereof;and a mechanism including contact means actuated by theelectro-receptive instrument and including relays controlled by saidcontact means, for operating said powered means in one direction or theother in response to said instrument being energized respectively lessthan or more than a predetermined extent which corresponds to saidpredetermined range of the variable, said mechanism and powered meanscontinually hunting; and an anticipator device for decreasing the periodof hunting of said mechanism and powered means.

26. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; a deflectable member; means foroscillating the deflectable member in response to said variable andproportionately with the value thereof; a mechanism for oscillating saidpowered means to shift the center point of its movement in one directionor the other in response to the center of movement of the deflectablemember being positioned respectively in or out of a predeterminedposition which corresponds to said predetermined range of the variable,said mechanism and powered means continually hunting; and an anticipatordevice for decreasing the period of hunting of said mechanism andpowered means.

27. Settable means for maintaining within any one of a plurality ofpredetermined ranges a variable regulated by a reversible controldevice, comprising reversible powered means for operating said controldevice; an electric instrument capable of oscillation; means forenergizing the electric instrument with a fluctuating current inresponse to said variable and proportionately with the value thereof, tocause oscillation of the instrument in step with the fluctuations of thecurrent, the period of oscillation of said instrument and fluctuation ofsaid current having a predetermined relationship to the value of thevariable; a mechanism for oscillating said powered means to shift thecenter point of its movement in one direction or the other in responseto said period of oscillation being respectively less than or more thana predetermined value; and manually operable means for altering therelationship between the period of oscillation of said instrument andthe value of the variable, thereby to change the range in which thevariable is to be maintained.

28. Settable means for maintaining with any one of a plurality ofpredetermined ranges a variable regulated by a reversible controldevice, comprising a reversible powered means for operating said controldevice; an electro-receptive instrument; means for energizing theelectroreceptive instrument in response to said variable andproportionately with the value thereof; an anticipator device forcausing oscillation of said instrument, the period of said oscillationhaving a predetermined relationship to the value of the variable; amechanism for operating said powered means in one direction or the otherin response to said period of oscillation being respectively less thanor more than a predetermined value, said mechanism and powered meanscontinually hunting; and manually operable means for altering therelationship between said period of oscillation and value of thevariable, thereby to change the range in which the variable is to bemaintained.

29. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptive instrumenthaving a deflectable member; means for energizing the electro-receptiveinstrument to deflect the member thereof in response to said variableand proportionately with the value thereof, said deflectable memberhaving a predetermined relationship to the value of the variablethroughout part of the range of the variable; a mechanism for operatingsaid powered means in one direction or the other in response to saidmember being deflected respectively less than or more than apredetermined extent which corresponds to said predetermined range ofthe variable, said powered means and deflectable member normallyhunting; and means responsive to movement of said powered means in onedirection for automatically producing a different predeterminedrelationship between the member and value of the variable, reversemovement of the powered means automatically restoring thefirst-mentioned predetermined relationship whereby the period of huntingof the powered means and member is decreased.

30. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptive instrumenthaving a deflectable member; means for energizing the electro-receptiveinstrument to deflect the member thereof in response to said variableand proportionately with the value thereof, said deflectable memberhaving a predetermined relationship to the value of the variablethroughout part of the range of the variable; a mechanism for operatingsaid powered means in one direction or the other in response to saidmember being deflected respectively less than or more than apredetermined extent which corresponds to said predetermined range ofthe variable, said powered means and deflectable member normallyhunting; and means responsive to movement of said powered means in onedirection for automatically producing a different predeterminedrelationship between the member and value of the variable, reversemovement of the powered means automatically restoring thefirst-mentioned predetermined relationship whereby the period of huntingof the powered means and member is decreased, the said mechanism foroperating the powered means including: a pair of screen grid vacuumtubes and circuits therefor, one of said tubes having its electrodespolarized, to render it normally conducting; and means, controlled bythe deflectable member, for polarizing the electrodes of the other tubeto render it either conducting or non-conducting, said tubes being sointerconnected that said one tube is rendered. non-conducting wheneverthe said other tube is conducting, and said interconnections including aconnection between the anode circuit of the one tube and the screen gridof the other tube, and including a connection between the anode circuitof the other tube and the screen grid of the one tube.

31. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptive instrumenthaving a deflectable member; means for energizing the electro-receptiveinstrument to deflect the member thereof in response to said variableand proportionately with the value thereof, said deflectable memberhaving a predetermined relationship to the value of the variablethroughout part of the range of the variable; a mechanism for operatingsaid powered means in one direction or the other in response to saidmember being deflected respectively less than or more than apredetermined extent which corresponds to said predetermined range ofthe variable, said powered means and deflectable member normallyhunting; and means responsive to movement of said powered means in onedirection and including a friction device, a contact actuated by thefriction device and a resistor connected with the electro-receptiveinstrument and under the control of said contact, for automaticallyproducing a different predetermined relationship between thedeflectaccent;

31 able member and value of the variable, reverse movement of thepowered means automatically restoring the first-mentioned predeterminedre lationship whereby the period of hunting of the powered means andmember is decreased.

32. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electric instrument having adeflectable member; means for energizing said instrument to deflect themember thereof in response to said variable and proportionately with thevalue thereof, said defiectable member having a predeterminedrelationship to the value of said variable thr-oughout part of the rangeof the variable; a selectively operable mechanism for oscillating saidpowered means to shift the center point of its movement in one directionor the other in response to said member being deflected respectivelyless than or more than a predetermined extent which corresponds to saidpredetermined range of the variable, said powered means and deflectablemember normally hunting; means, connected with said mechanism forautomatically producing a different predetermined relationship betweenthe member and value of the variable when the selected operation of themechanism is changed to reverse the powered means, resumption oforiginal operation of the said mechanism acting to restore thefirst-mentioned predetermined relationship; and means responsive tomovement of said powered means in one direction for automaticallyproducing a second different predetermined relationship between thedeflectable member and value of the variable, reverse movement of thepowered means acting to restore the firstmentioned relationship, saidmeans for automatically producing different predetermined relationshipsdecreasing the period of hunting of the powered means and member.

33. Means for maintaining Within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptive instrumenthaving a deflectable member; means for energizing the electro-receptiveinstrument to deflect the member thereof in response to said variableand proportionately with the value thereof, said member having apredetermined relationship to the value of said variable throughout partof the range of the variable; means for operating said powered means inone direction or the other in response to said member being deflectedrespectively less than or more than a predetermined extent whichcorresponds to said predetermined range of the variable, said poweredmeans and member continually hunting; means responsive to movement ofsaid powered means in one direction for automatically producing adifferent predetermined relationship between the deflectable member andvalue of the variable, reverse movement of the powered meansautomatically restoring the firstmentioned predetermined relationshipwhereby the period of hunting of the powered means and member isdecreased; and means responsive to said powered means attaining apredetermined limiting position for automatically rendering said poweredmeans inoperative for movement beyond said position.

34. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptiveinstrument; means for energizing the electro-receptive instrument inresponse to said variable and proportionately with the value thereof;means for operating said powered means in one direction or the other inresponse to said instrument being energized respectively less than ormore than a predetermined extent which corresponds to said predeterminedrange of the variable; and safety means operative upon the variableattaining a predetermined extreme value for operating the said poweredmeans solely in one direction and independently of operation of saidelectro-receptive instrument 35. Means for maintaining within apredetermined range a variable regulated by a reversible control device,comprising reversible powered means for operating said control device;an electric instrument; means for energizing said instrument in responseto said variable and propcrtionately with the value thereof; means foroscillating said powered means to shift the center point of its movementin one direction or the other in response to said instrument beingenergized respectively less than or more than a predetermined extentwhich corresponds to said predetermined range of the variable; andsafety means operative upon the variable attaining a predeterminedextreme value for operating the said powered means solely in onedirection and independently of operation of said electric instrument,said safety means comprising a second electric instrument energized fromthe same source as the first-mentioned instrument, and comprising acircuit control device connected with the means for operating thepowered means.

36. Means for maintaining within a predetermined range a variableregulated by a reversible control device, comprising reversible poweredmeans for operating said control device; an electro-receptiveinstrument; means for energizing the electro-receptive instrument inresponse to said variable and proportionately with the value thereof;means for operating said powered means in one direction or the other inresponse to said instrument being energized respectively less than ormore than a predetermined extent which corresponds to said predeterminedrange of the variable; and safety means including a secondelectro-receptive instrument energized in response to said variable andproportionately with the value thereof for operating the said poweredmeans solely in one direction and independently of operation of saidfirst-mentioned electro-receptive instrument, said safety means beingoperative upon the variable attaining a predetermined extreme value.

3'7. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible, powered actuator device for moving the member in onedirection or the other in response to an increase or decreaserespectively in the value of said variable whereby the variable ismaintained within a predetermined range, the response of said actuatordevice to the variable involving a time lag and said reversibly movablemember and actuator device continually hunting; and a mechanismresponsive to a relatively small movement of said member in onedirection or the other for operating the actuator device in the samesense as and prior to the operation it would normally have in respondingto the change in the variable due to a greater movement of the mem berin said directions respectively, thereby to decrease the period ofhunting of the member and actuator device.

38. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible powered actuator device for moving the member in onedirection or the other in response to an increase or decreaserespectively in the value of said variable whereby the variable ismaintained within a predetermined range, the response of said actuatordevice to the variable involving a time lag and said reversibly movablemember and actuator device continually hunting; and a mechanismresponsive to a relatively small movement of said member in onedirection or the other and including a movable contact, a friction drivebetween the member and the contact, and including a resistor connectorwith said actuator device and controlled by said contact, for operatingthe actuator device in the same sense as and prior to the operation itwould normally have in responding to the change in the variable due to agreater movement of the member in said directions respectively, therebyto decrease the period of hunting of the member and actuator device.

39. In an automatic control device, a reversibly movable member; meansfor controlling a vari able in response to movement of said member; areversible powered actuator device for moving the member in onedirection or the other in response to an increase or decreaserespectively in the value of said variable whereby the variable ismaintained within a predetermined range, said reversibly movable memberand actuator device continually hunting; and a mechanism responsive to arelatively small movement of said member in one direction or the otherfor operating the actuator device in the same sense as the actuation itwould normally have in responding to the change in the variable due to agreater movement of the member in said directions respectively, therebyto decrease the period of hunting of the member and actuator device.

40. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible powered actuator device for moving the member in onedirection or the other proportionately in response to an increase ordecrease respectively in the value of said variable whereby the variableis maintained within a predetermined range, the response of saidactuator device to the variable involving a time lag and said reversiblymovable member and actuator device continually hunting, said actuatordevice including a translating device actuated by the variable, andincluding a relay; and means responsive to energization of said relayfor automatically reversing the operation of the actuator device,deenergization of said relay automatically restoring the forwardoperation of the actuator device thereby to decrease the period ofhunting of the member and actuator device.

41. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible powered actuator device for oscillating the member to shiftthe center point of its movement in one direction or the otherproportionately in response to an increase or decrease respectively inthe value of said variable whereby the variable is maintained within apredetermined range, the response of said actuator device to thevariable involving a time lag and said reversibly movable member andactuator device continually hunting, said actuator device including atranslating device actuated by the variable, and including a relay; andmeans responsive to energization of said relay and including a contactand a resistor connected to said contact and to the translating device,for automatically reversing the operation of the actuator device,deenergization of said relay automatically restoring the forwardoperation of the actuator device thereby to decrease the period ofhunting of the member and actuator device.

42. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible powered actuator device for moving the member in onedirection or the other proportionately in response to an increase ordecrease respectively in the value of said variable whereby the variableis maintained within a predetermined range, the response of saidactuator device to the variable involving a time lag and said reversiblymovable member and actuator device continually hunting; and ananticipator mechanism responsive to forward operation of the actuatordevice for reversing the operation thereof, said anticipator mechanismresponding to reverse operation of the actuator device by restoringforward operation thereof, thereby to decrease the period of hunting ofthe member and the actuator device.

43. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; areversible powered actuator device for moving the member in onedirection or the other proportionately in response to an increase ordecrease respectively in the value of said variable whereby the variableis maintained within a predetermined range, the response of saidactuator device to the variable involving a time lag and said reversiblymovable member and actuator device continually hunting; and ananticipator mechanism operated by a predetermined minute amount offorward operation of the actuator device for reversing the operationthereof, said anticipator mechanism being operated by a predeterminedminute amount of reverse operation of the actuator device to restoreforward operation thereof, thereby to decrease the period of hunting ofthe member and the actuator device.

44. In an automatic control device, a reversibly movable member; meansfor controlling a variable in response to movement of said member; aselectively operable powered actuator device for moving the member inone direction or the other proportionately in response to an increase ordecrease respectively in the value of said variable whereby the variableis maintained within a predetermined range, the response of saidactuator device to the variable involving a time lag and said reversiblymovable member and actuator device continually hunting; a mechanismresponsive to one selected operation of the actuator device forautomatically changing to another selected operation thereof, saidmechanism responding to said other selected operation of the actuatordevice by restoring said one selected operation thereof; and a mechanismresponsive to movement of said member in one direction for automaticallychanging to said other selected operation of the actuator device, saidsecondmentioned mechanism responding to movement of the member in theopposite direction by restoring said one selected operation of theactuator device, and both said mechanisms acting to decrease the periodof hunting of the member and actuator device.

45. An automatic control for use with an instrumentality heated by aheating medium, comprising a reversible control device for said medium;reversible powered means for operating said control device; a sensitiveelectric-instrument movement havng a defiectable member; means forenergizing the instrument movement with an oscillating current which isresponsive to and proportionate with heating of said instrumentality,the response of the instrument movement to a change of temperature ofsaid instrumentality involving a time lag; means for oscillating saidpowered means to shift the center point of its movement in one directionor the other in response to the center movement of the defiectablemember occupying respectively one position or a different position, saidcontrol device and powered means continually hunting; and anticipatormeans increasing the speed of said hunting beyond the normal for saidcontrol device and powered means.

46. A settable automatic control for use with an instrumentality heatedby a heating medium, comprising a reversible control device for saidmedium; reversible powered means for operating said control device; asensitive electric-instrument movement having a defiectable member;means for energizing the instrument movement responsive to andproportionate with heating of said instrumentality, the range ofmovement of the defiectable member having a predetermined relationshipto the temperature of said instrumentality throughout part of the rangeof said temperature; means for oscillating said powered means to shiftthe center point of its movement in one direction or the other inresponse to the center of movement of the defiectable member beingrespectively in an advanced or a retracted position, said central deviceand powered means continually hunting; and manually settable means foraltering said relationship between the member and temperature of theinstrumentality, thereby to change the conditions to be maintained bythe control.

47. An automatic control device for use with an instrumentality heatedby a heating medium, comprising a reversible control device for saidmedium; reversible powered means for operating said control device; asensitive electric-instrument movement having a defiectable member;means for operating said powered means in one direction or the other inresponse to the deflectable member being respectively in an advanced ora retracted position; means for energizing the instrument movement inresponse to and proportionately with heating of said instrumentality,the response of the instrument movement to a change of temperature ofsaid instrumentality involving a time lag, and the defiectable memberhaving a predetermined relationship to the temperature of saidinstrumentality throughout part of the range of said temperature, saiddefiectable member and powered means continually hunting; and meansresponsive to movement of said powered means in one direction forautomatically producing a diiferent predetermined relationship betweenthe defiectable member and the temperature of the instrumentality,reverse movement of the powered means automatically restoring thefirst-mentioned predetermined relationship whereby the period of huntingof the defiectable member and powered means is decreased.

4B. A settable automatic control device for use with an instrumentalityheated by a heating medium, comprising a reversible control device forsaid medium; reversible powered means for operating said control device;a defiectable member; means for operating said powered means in onedirection or the other in response to the defiectable member beingrespectively in an advanced or a retracted position; means fordeflecting the defiectable member in response to and proportionatelywith heating of said instrumentality, the response of the member to achange of temperature of said instrumentality involvin a time lag, andthe member having a predetermined relationship to the temperature ofsaid instrumentality throughout part of the range of said temperature,said defiectable member and powered means continually hunting; manuallysettable means for altering said relationship, thereby to change theconditions to be maintained by the control; and means responsive tomovement of said powered means in one direction for automaticallyproducing a difi'erent predetermined relationship between thedefiectable member and the temperature of the instrumentality, reversemovement of the powered means automatically restoring thefirst-mentioned predetermined relationship whereby the period of huntingof the defiectable member and powered means is decreased.

49. A settable automatic control device for use With an instrumentalityheated by combustion of fuel, comprising fuel flow-control means;reversible powered means for operating said flow-control means toincrease or decrease the fuel flow; a defiectable member; means foroscillating the defiectable member in response to and proportionatelywith heating of said instrumentality, the center of movement of themember having a predetermined relationship to the temperature of saidinstrumentality throughout a part of the range of said temperature;manually settable means for altering said relationship, thereby tochange the conditions to be maintained by the control device and meansfor oscillating said powered means to shift the center point of itsmovement in one direction or the other in response to the center ofmovement of the defiectable member being positioned in or out of apredetermined position respectively.

50. An automatic control device for use with an instrumentality heatedby combustion of fuel, comprising fuel flow-control means; reversiblepowered means for operating said flow-control means to increase ordecrease the fuel flow; a deflectable member; means for operating saidpowered means in one direction or the other in response to thedefiectable member being positioned in or out of a predeterminedposition respectively; means for deflecting the defiectable member inresponse to and proportionately with heating of said instrumentality,the member having a predetermined relationshi to the temperature of saidinstrumentality throughout a part of the range of said temperature, theresponse of the member to a change of temperature of saidinstrumentality involving a time lag, and said defiectable member andpowered means continually hunting; and means responsive to movement ofsaid powered means in one direction for automatically producing adifferent predetermined relationship between the member and thetemperature of the instrumentality, reverse movement of the poweredmeans automatically restoring the first-mentioned predetermined re-

